1. Field of the Invention
The present invention relates to a steering device for a vehicle, and more particularly, to a steering device having a sub-steering mechanism that is required upon conducting automatic steering for compensating a steering amount of a steering wheel performed by a driver, or required for steering upon the automatic driving, for example.
2. Description of the Related Art
Control methods relating to steering of vehicles have been proposed in which, for example, auxiliary automatic control of the direction of wheels is performed so as to optimize steering characteristics, i.e., change in an actual traveling direction of a vehicle with respect to the amount of turning of a steering wheel, or an automatic control operates instead of operation by a driver to drive and control a steering system so that a running position of a vehicle is within a predetermined lane.
The applicant of the present invention filed an application for a patent for a steering device for a vehicle such as shown in FIG. 11 (Japanese Patent Application No. 2001-353130) to perform this kind of wheel steering angle control for a vehicle.
The conventional steering device for a vehicle will be described with reference to FIG. 11 showing a construction of the device.
In FIG. 11, a steering wheel operated by a driver is indicated by reference numeral 1 and a first planetary gear mechanism is indicated by reference numeral 2. The first planetary gear mechanism 2 is constituted by a sun gear 201 connected to the steering wheel 1, planetary gears 202a and 202b supported by a carrier 203, a ring gear 204, and a worm wheel 205 for rotating the ring gear 204.
A second planetary gear mechanism indicated by reference numeral 3 in FIG. 11 is also provided. The second planetary gear mechanism 3 is constituted by a sun gear 301, planetary gears 302a and 302b supported on a carrier 303, and a fixed ring gear 304. A shaft indicated by reference numeral 4 connects the carrier 203 of the first planetary gear mechanism 2 and the carrier 303 of the second planetary gear mechanism 3 to each other. The first planetary gear mechanism 2 or the combination of the first planetary gear mechanism 2 and the second planetary gear mechanism 3 is a sub-steering mechanism capable of mechanically adding an auxiliary steering angle to a turning angle of the steering wheel 1.
A rack-and-pinion steering mechanism indicated by reference numeral 5 in FIG. 11 is also provided. The rack-and-pinion steering mechanism 5 is constituted by a rack-and-pinion 501, and a worm wheel 502 capable of reversing the rotation direction and that is used to rotate the pinion 501 with an electric motor 901 used as a wheel steering angle control actuator. Knuckle arms are indicated by reference symbols 6a and 6b, and wheels to be turned for steering are indicated by 7a and 7b. 
A reaction control mechanism indicated by reference numeral 8 in FIG. 11 is a mechanism for giving the steering wheel 1 a reaction torque by applying a drive torque to the first planetary gear mechanism 2 operating as the sub-steering mechanism. The reaction control mechanism 8 is constituted by a reaction motor 801 for applying the drive torque to the first planetary gear mechanism 2, and a worm gear 802 which meshes with the worm wheel 205 of the first planetary gear mechanism 2. The worm gear 802 cannot be rotated by the rotation of the worm wheel 205. That is, the reaction mechanism can be self-locked.
A wheel steering angle control mechanism indicated by reference numeral 9 in FIG. 11 is a mechanism for driving the steering mechanism 5. The wheel steering angle control mechanism 9 is constituted by an electric motor 901 and a worm gear 902 which meshes with the worm wheel 502 of the steering mechanism 5. The combination of the worm wheel 502 and the worm gear 902 is such that the worm gear 902 can be rotated from the worm wheel 502 side, that is, it can be reversely rotated.
A reaction torque detection means for detecting the reaction torque produced at the steering wheel 1 is indicated by reference numeral 10 in FIG. 11. A wheel steering angle detection means 11 for detecting the wheel steering angle of the wheels turned for steering 7a and 7b and a steering wheel steering angle detection means 12 for detecting the steering angle of the steering wheel 1 are also provided.
A target wheel steering angle production means is indicated by reference numeral 13 in FIG. 11. The target wheel steering angle production means 13 produces a target wheel steering angle 1301 by computing a necessary wheel steering angle, for example, from an output 1201 from the steering wheel steering angle detection means 12, a steering request 20 from another system (e.g., a lane keeping device), and a vehicle state signal 21 (e.g., a vehicle speed signal, a yaw rate signal, or the like).
A wheel steering angle control means is indicated by reference numeral 14 in FIG. 11. The wheel steering angle control means 14 controls the wheel steering angle of the wheels turned for steering 7a and 7b by driving the wheel steering angle control electric motor 901 so that the target wheel steering angle 1301 and an output 1101 from the wheel steering angle detection means 11 are equal to each other.
A target reaction production means for setting a target value of the reaction torque received by the driver through the steering wheel 1 is indicated by reference numeral 15 in FIG. 11. The target reaction production means 15 computes a suitable reaction, for example, from the output 1201 from the steering wheel steering angle detection means 12 and the vehicle state signal 21 (e.g., a vehicle speed signal, a yaw rate signal, or the like) to produce a target reaction torque 1501.
Further, a reaction torque control means is indicated by reference numeral 16 in FIG. 11. The reaction torque control means 16 controls the reaction torque produced in the steering wheel 1 by driving the reaction electric motor 801 so that the target reaction torque 1501 and an output 1001 from the reaction torque detection means 10 are equal to each other.
As described above, the conventional device controls the wheel steering angle by computing a suitable wheel steering angle, for example, from the operation of the steering wheel 1 performed by the driver and a signal from another system, and simultaneously controls production of the steering wheel reaction in the steering wheel 1 by computing a suitable steering reaction.
However, if the wheel steering angle and the steering wheel reaction are independently controlled in the device having the above-described sub-steering mechanism, as shown in FIG. 2, a drive torque is required for the wheel steering angle control electric motor 9. That is, according to the balance about the wheel steering angle control electric motor (wheel steering angle control mechanism) 9, a drive torque (Ta+Tb) for a self-alignment torque (road surface reaction) Ta produced in the wheels turned for steering and a torque Tb distributed from the reaction electric motor 8 by the sub-steering mechanisms (planetary gear mechanisms) 2 and 3 is required of the wheel steering angle control electric motor 9.
On the other hand, according to the balance about the reaction electric motor (reaction control mechanism) 8, a drive torque (Tb+Tc) for a reaction torque Tc produced in the steering wheel 1 and Tb distributed by the sub-steering mechanisms 2 and 3, is required for the reaction electric motor 8.
Thus, the steering system using the above-described steering device has a problem in that it consumes a larger amount of energy in comparison with the ordinary power steering system. For ease of description, the gear ratios of the planetary gear mechanisms 2 and 3, the gear ratio of the steering mechanism 5, and so on have been shown in a converted state on one steering axis.
In view of the above-described problem of the conventional art, an object of the present invention is to provide a steering device for a vehicle which has a sub-steering mechanism, in which a wheel steering angle and a steering wheel reaction are controlled independently of each other, and in which energy consumption can be reduced.
To achieve the above-described object, according to the present invention, there is provided a steering device for a vehicle having: a steering wheel operated by a driver; a sub-steering mechanism for mechanically adding an auxiliary steering angle to a turning angle of the steering wheel; a steering mechanism for steering wheels turned for steering; a reaction control mechanism for giving the steering wheel a reaction torque by energizing the sub-steering mechanism with a drive torque; a wheel steering angle control mechanism for driving the steering mechanism; a reaction torque detection means for detecting the reaction torque produced in the steering wheel; and a wheel steering angle detection means for detecting wheel steering angles of the wheels turned for steering.
Further, the steering device for a vehicle having: a steering wheel steering angle detection means for detecting a steering wheel angle when the steering wheel is operated; a target wheel steering angle production means for producing a target wheel steering angle on the basis of the steering wheel angle detected by the steering wheel steering angle detection means; and a wheel steering angle control means for controlling the wheel steering angles of the wheels turned for steering by driving the wheel steering angle control mechanism so that the wheel steering angles detected by the wheel steering angle detection means and the target wheel steering angle produced by the target wheel steering angle production means coincide with each other.
In addition, the steering device for a vehicle having: a target reaction production means for producing a target reaction on the basis of the steering wheel angle detected by the steering wheel steering angle detection means; a first reaction torque control means for controlling the reaction torque produced in the steering wheel by driving the reaction control mechanism so that the reaction torque detected by the reaction torque detection means and the target reaction produced by the target reaction production means coincide with each other; a second reaction torque control means for compensating an output from the wheel steering angle control means so that the reaction torque detected by the reaction torque detection means and the target reaction produced by the target reaction production means coincide with each other; a reaction control limitation means for limiting an output from the first reaction torque control means on the basis of a limit value; and a limit range setting means for setting the limit value used by the reaction control limitation means.
The above-described steering device has the effect of reducing energy consumption.